1. Field of the Invention
The present invention relates, in general, to equipment for cleaning steam generators and, in particular, to sludge lance nozzles used in articulated fluid sludge lances used to clean boiler tube lanes from the annular openings found in such boilers.
2. Description of the Related Art
In nuclear power stations, steam generators, such as recirculating steam generators and once-through steam generators, are used for heat exchange purposes to generate steam which drives turbines. Primary fluid is heated in the core of the nuclear reactor and passed through a bundle of tubes in the steam generator. Secondary fluid, generally water, is fed into the space surrounding the tubes and receives heat from the tubes converting the water into steam for driving the turbines. After cooling and condensation has occurred, the secondary fluid is directed back into the space around the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating conditions, sludge accumulates on the lower portions of the tubes and on the tubesheet which supports same. The sludge is mainly comprised of an iron oxide, such as magnetite and reduces the heat transfer efficiency of the tubes as well as causing corrosion. Thus, the tubes must be cleaned periodically to remove the sludge. Various types of apparatus and methods are available to accomplish this task. The sludge buildup is extremely difficult to remove and concentrated high pressure fluid streams are used to remove this sludge using sludge lances from either a no-tube lane or annular opening of the boiler. Pressure of 8,000 p.s.i. at the spray nozzle, normal. This high pressure makes it imperative to use a balanced nozzle having identical nozzles at opposing ends of the lance to minimize stress on the equipment. Balanced flow nozzles are known and examples of same may be found in the following prior art references.
U.S. Pat. No. 4,980,120 entitled "Articulated Sludge Lance" assigned to the assignee of the present invention, and hereby incorporated by reference, discloses an articulated lance for cleaning sludge located between steam generator tubes. In operation, the lance is inserted through a handhole in the no-tube lane of the boiler.
U.S. Pat. No. 5,194,217 entitled "Articulated Sludge Lance with a Movable Extension Nozzle" is also assigned to the assignee of the present invention, and hereby incorporated by reference, it discloses an articulated sludge lance with a retractable movable extension nozzle.
In addition to those references, U.S. Pat. No. 4,407,236 to Schukei, et al discloses a thin strip of spring steel which enters a tube lane for sludge lance cleaning for nuclear steam generators. The forward ends of the capillary tubes located on the spring steel strips are directed downward for the jetting of fluid under high pressure.
U.S. Pat. No. 4,827,953 to Lee is directed to a flexible lance for steam generator secondary side sludge removal. This patent discloses a flexible lance having a plurality of hollow, flexible tubes extending lengthwise along the flexible member. There are a plurality of nozzles at an end of the flexible members with the flexible member being configured to go into the difficult to access geometry of the steam generator. The tight quarters of this particular type of lancing along with the need to provide an effective nozzle output which will remove the baked on sludge makes it difficult to provide an effective high pressure balanced nozzle assembly. Usually an effective nozzle takes up most of the allotted space for the lance making it impossible to provide two such nozzles in balanced opposition.
Thus, there is a need for an efficient balanced sludge lance nozzle for a sludge lancing apparatus which would effectively clean the tube lanes of a steam generator from any one of the access holes in a steam generator and especially lances entering from the annular chamber around the tubesheet of the boiler to clean the tubes therefrom.